The present invention relates to a valve control technique for controlling operations of valves provided in supply tube paths used to guide fluids such as medical fluids.
Begining to the semiconductor wafer manufacturing technique, in manufacturing processes in the various technical fields such as the LCD (liquid crystal display) substrate manufacturing technique, the magnetic disk manufacturing technique, and the multi-layer wiring pattern substrate manufacturing technique, there are utilized such chemical medical fluids as photoresist fluids, spinion glass fluids, polyimid resin fluids, pure water, developing fluids (alkalic medical fluids) etching fluids (acid medical fluids), and organic solvent. These medical fluids own various coefficients of viscosity from low coefficients to high coefficients. The fluid supply unit such as the pump is connected with the fluid flow-out unit such as the nozzle by the fluid supply tube path. In this fluid supply tube path, there is provided a valve for controlling the fluid such as the medical fluid flowing through this fluid supply tube path, namely for controlling the flow of the fluid member.
In the above-described various technical fields, not only impurities such as articles and bubbles are required not to be mixed into the fluid member, but also the valve for supplying a predetermined amount of the fluid member in high precision must be controlled under better precision. For instance, in the resist fluid supply control apparatus for dripping the photoresist fluid onto the surface of the semiconductor wafer, the switch valve must be employed so as to control opening/closing operations of the resist supply dripping nozzle by opening/closing the tube path for supply the fluid member, and furthermore it is required to prevent the resist fluid from being leaked from the dripping nozzle when the fluid dripping is stopped.
To avoid that unwanted articles are mixed into the supplied medical fluid such as the resist fluid, the filter, pump and control valve are combined in an integral form so as to reduce the fluid reserved amount within the fluid supply system, thus constituting the pump containing the filter, as described in JP-A-64-500135.
Moreover, JP-A-2-81630(U) discloses such a suck-back valve for sucking back the medical fluid into the dripping nozzle when the supply of the medical fluid is stopped in order to prevent the fluids from being leaked from the dripping nozzle after the medical fluid has been supplied.
In the former-mentioned medical fluid supply control apparatus as described in JP-A-64-500135, the diaphragm film is pressured, or controlled under negative pressure, so as to deform/control this diaphragm film, and such a valve is employed by which the supply of medical fluids from the flow path formed by the diaphragm film is performed/interrupted.
Since the compressed control member such as air is directly given to the diaphragm film so as to control the pressure in this valve, it is no possible to absorb the pressure variations of the fluid member produced in conjunction with the hammering phenomenon occurred in the medical fluid when the valve is open/closed. Therefore, erroneous operation of the valve is caused by the hammering phenomenon, so that the valve is mistakenly open/closed, resulting in various fluid dripping problems. Moreover, since the flow path structure of the valve is folded, the cavitation phenomenon happens to occur when the medical fluid is supplied, so that bubble would be produced and qualities of the medical fluids would be deteriorated.
In the latter-mentioned fluid-droplet preventing apparatus described in JP-A-2-81630(U), the air pressure valve effect to the suck-back valve body having the diaphragm film structure is controlled by the electric/air converting regulator, so that the operation speed and the operation amount of the suck-back valve body are controlled.
This control method corresponds to such a method for controlling pressure of the compressed air given to the suck-back valve unit in order to control the operation speed and the operation amount of the suck-back valve body. Similar to the above-described medical fluid supply control apparatus described in JP-A-64-500135, it is not possible to absorb variations in the fluid pressure in conjunction with the hammering phenomenon occurred when another fluid supply valve constructed in the fluid supply system is open/closed. Thus, the suck-back operation timing of the suck-back valve body having the diaphragm film structure is mistakenly performed due to the hammering phenomenon, and furthermore, the suck-back valve body is erroneously operated due to the insufficient suck-back operation speed, resulting in various fluid dripping problems.
As described above, in the conventional technical methods, the operation of the valves for controlling the supply of the fluid member such as the medical fluid cannot be controlled in high precision, so that various fluid dripping problems are caused by mistakenly operating the valves. As a consequence, Inventors of the present invention could confirm that a predetermined amount of fluid members cannot be supplied while maintaining high purity of the fluid members.
FIG. 1 schematically shows a valve under develop as a comparison example. This valve is provided in a supply tube path for connecting a pump (not shown) for supplying a medical fluid as a fluid member with an exhaust unit for exhausting the fluid member. The valve is employed so as to open/close the supply tube path. As indicated in FIG. 1, a flow-in-side tube path 2 and a flow-out-side tube path 3 are provided in a housing 1, and a diaphragm type valve body 4 is mounted on this housing 1 in order to open/close both of the flow paths.
To open/close this valve body 4, a piston 5 having a piston rod 5a is movably provided within the housing 1 along the shaft direction. A coil spring 6 is employed in the piston 5, which may give spring force to close the valve body 4. This piston 5 is operable in response to the air pressure supplied/exhausted from two supply/exhaust ports 7 and 8 connected to the housing 1.
Similar to the above-mentioned prior art, when the supply of the fluid member such as the medical fluid is controlled by the switch valve having such a structure, erroneous operations of this valve happen to occur, resulting in various fluid dripping problems. The causes of these problems may be revealed.
To find out the causes, a drive model of the valve operation mechanism unit for operating the valve body 4 shown in FIG. 1 is schematically illustrated in FIG. 2. As shown in this drive mode, it is conceivable that the valve mechanism unit V to achieve the valve function for opening/closing the supply of the fluid member L owns an elastic body S having the spring constant K containing the valve body 4 shown in FIG. 1 and the coil spring 6. This valve mechanism unit V is deformed by the air pressure. As a means for controlling deformation of this valve mechanism unit V, the air pressure is effected from a valve drive operation point P.
As represented in this drive model, when a temporal pressure variation .DELTA.P1 is produced in the fluid member L, a displacement amount X1 of the valve mechanism unit V in proportion to this pressure variation .DELTA.P1 is produced. In this type of valve mechanism unit V, the absorption of the energy amount with respect to the displacement amount X1 of the valve mechanism unit V when the temporal pressure variation .DELTA.P1 is produced in the fluid member L may exist as only the absorption of the energy amount caused by the spring deformation only with the spring constant K.sub.V1 constituted by the valve mechanism unit V.
Accordingly, a relative formula concerning the energy amount absorption of the pressure variation amount .DELTA.P1 of the fluid member L is expressed as follows: EQU .DELTA.P1=K.sub.V1 .times.X.sub.1.
In this formula, symbol .DELTA.P1 denotes the pressure variation amount of the fluid member L, symbol K.sub.V1 represents the spring constant of the valve mechanism unit V, and symbol X.sub.1 shows the displacement amount of the valve mechanism unit V.
It could be understood from such a relative formula that the pressure variation amount .DELTA.P.sub.1 of the fluid member is directly connected to the energy conversion of the displacement amount X.sub.1 of the valve mechanism unit V by way of the linear formula. As a consequence, when such a valve as shown in FIG. 1 is employed so as to control the supply of the fluid member such as the medical fluid, the valve mechanism unit V itself would be deformed by receiving the pressure variations in the fluid member flowing through the tube path, and thus the valve is erroneously operated.
In FIG. 3 there is shown a medical fluid supply control apparatus such that both of a switch valve 13 operable by air pressure, namely the valve having the same structure as FIG. 1, and also a suck-back valve 14 having a similar structure thereto are provided in a medical fluid supply tube path 12a which is employed so as to couple a medical fluid supply unit 10 with a dripping nozzle for supplying the medical fluid to the semiconductor wafer W. The switch valve 13 is operable in response to the pressure of air supplied from an air supply source 15 via a flow rate control valve 16. The supply of the air pressure to the switch valve 13 is controlled by way of an electromagnetic valve 17 operated by a solenoid and provided in an air pressure distribution tube 12b. The supply of electric power to the solenoid of the electromagnetic valve 17 is controlled in response to ON/OFF signals derived from a power source 18.
On the other hand, as represented in FIG. 3, after the spraying operation of the medical fluid from the dripping nozzle 11 to the semiconductor wafer W has been accomplished, the suck-back valve 14 is provided in the medical fluid supply tube path 12a in order that the medical fluid is sucken back to the dripping nozzle 11 to thereby preventing the fluid dripping. This suck-back valve 14 is operable in response to the compressed air which is fed from the air pressure source 15a via the air pressure distribution tube 12c. In this air pressure distribution tube 12c, there are provided a regulator for setting pressure of the compressed air derived from the air pressure source 15a to a preselected pressure value, and also a speed (velocity) control valve 20 for controlling a flow speed of the compressed air.
FIG. 4 is a timing chart for indicating operation conditions of the switch valve 13 employed in the medical supply control apparatus shown in FIG. 3. Under such a condition that no electric power is supplied to the electromagnetic valve 17, the switch valve 13 is normally closed. In other words, the medical fluid from the medical fluid supply unit 10 is not yet supplied to the dropping nozzle 11. Under this condition, when the ON signal is supplied from the power source 18 to the electromagnetic valve 17, the compressed air supplied from the air pressure source 15 is supplied via the air pressure distribution tube 12bto the switch valve 13, so that the switch valve 13 is changed from the close state into the upon state.
As the switching operation timing, a delay time D1 is produced after the electromagnetic valve 17 is changed from the OFF state into the ON state until the switch valve 13 starts its operation. Thereafter, an operation time D2 is produced until the opening operation of the switch valve 13 is ended, so that the opening operation of the switch valve 13 is complete. Also when the switch valve 13 is open and then closed, a similar delay time and a similar operation time are produced.
It could be recognized that both of the delay time D1 and the operation time D2 when the open state of the switch valve 13 is changed into the close state are varied based on the open-degree control amount for the flow-rate control valve 16 in the case that the supply amount containing the pressure of the compressed air derived from the air pressure source 15 is maintained at constant.
A table 1 indicates measurement results as to the delay time D1 and the operation time D2 while the control amount of the flow-rate control valve 16, i.e., the rotation amount of the control knob is varied.
TABLE 1 ______________________________________ control amount of flow-rate control valve 16 0.5 turn 1.0 turn 1.5 turns ______________________________________ delay time D1 (sec) of switch valve 13 0.52 0.22 0.17 operation time D2 (sec) of switch valve 13 0.37 0.19 0.13 total time 0.89 0.41 0.30 ______________________________________
As described above, in the medical fluid supply control apparatus of FIG. 3 with employment of the switch valve 13 similar to the valve shown in FIG. 1, the opening degree of the flow-rate control valve 16 must be manually controlled. Thus, there is a fluctuation in this control amount, so that a total time after the ON/OFF operation timing of the electromagnetic valve 17 until the close operation of the switch valve 13 is accomplished differs from each other.
When the opening degrees of the flow-rate control valve 16 are different from each other, the opening/closing operation times of this switch valve 13 are different from each other, so that the supply speeds of the medical fluid supplied from the dripping nozzle 11 to the semiconductor wafer W are different from each other. As a consequence, in the actual medical fluid supply stem, as explained before, the opening/closing operation times of the switch valve 13 are different from each other even by the medical fluid pressure variation amount caused by the hammering phenomenon which occurs when the other switch valve 13 is open/closed. In connection thereto, the supply speeds of the medical fluid from the dripping nozzle 11 via the switch valve 13 would be different from each other.
As a result, various fluid dripping problems may be produced due to erroneous operations of the switch valve 13. Therefore, the above-described problems may be emphasized in such a medical fluid supply system with employment of large quantities of switch valves.
FIG. 5A, FIG. 5B and FIG. 5C schematically illustrate various conditions when the suck-back operation is accomplished by operating the suck-back valve 14 after the spraying operation of the medical fluid by the dripping nozzle 11 is ended, i.e., FIG. 5A shows the normal suck-back operation, and FIGS. 5B, 5C indicate the abnormal suck-back operations. More specifically, FIG. 5A shows such a condition that the medical fluid is drawn into the dripping nozzle 11 when the suck-back speed is performed at the normal speed. FIG. 5B indicates such a state that bubble is produced in the drawn medical fluid when the suck-back speed is increased. FIG. 5C represents such a condition that the suck-back speed is delayed, so that the suck-back function cannot be achieved and then spray fluctuation occurs.
As described above, after the medical fluid has been sprayed from the dripping nozzle 11, if the sprayed medical fluid is not sucken at the proper timing and the proper speed in high precision into the dripping nozzle 11, then the spray fluctuation happens to occur, so that the process yield of the semiconductor wafer would be lowered.